Acid catalyzed esterification of cellulose pretreated with an nu, nu-dialkyl amide



ACID CATALYZED ESTERIFICATION OF CELLU- kOSE EPRETREATED WITH AN N,N-DIALKYL Roe C. Blume, Waynesboro, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware N Drawing. Application February 8,

Serial No. 270,772

Claims. (Cl. 260229) This invention relates to the production of organic esters of cellulose. More specifically, it relates to a process which permlts a rapid, high temperature esterification of cellulose which yields a product of uniform solubility, good filterability and high molecular weight.

Cellulose is usually esterified by the slow addition at elevated temperature of an acid anhydride to a slurry of cellulose in anhydrous acid. A strong inorganic acid is incorporated in the reaction mixture as a catalyst. It has been observed that extended contact with such strong inorganic acid even in catalytic amounts causes degradation of the cellulose molecule, especially at relatively high reaction temperatures. Excessive degradation results in depolymerization of the cellulose molecule to such an extent that the fihns and filaments produced from the final ester are of a quality and strength too low for practical purposes. When rapid addition of the acid anhydride is resorted to in an effort to reduce the period during which the reaction progresses under degrading conditions local reaction and spot heating ocunder esterification conditions. One such activation procedure consists in heating the cellulose in a bath of anhydrous (glacial) acetic acid or other carboxylic acid as a diluent and solvent to which a minor amount of anhydride to carry acetylation to completion, i. e., cellulose triacetate.

The following examples illustrate a method of carrying out the process. They are presented merely by way of illustration and not by way of limitation. Where the value relative viscosity is reported, it refers to that value obtained by dividing the viscosity at C. of a 0.095% solution in 92% aqueous acetic acid by the viscosity at the same temperature of 92% aqueous acetic acid.

Example I Five (5) grams of cotton linters are added to 100 grams of dimethylformamide. Agitation is provided and invention to provide a t 2,705,710 Patented Apr. 5, 1955 the resultant slurry is heated to a temperature of 140 After 10 minutes at temperature, 25 grams of hot acetic anhydride is stirred in. This is followed by 0.3 gram of concentrated sulfuric acid. The reaction requires about four minutes after addition of the catalyst.

Example 11 Five (5) grams of cotton linters are added to grams of dimethylformamide. The slurry is agitated and heated to C Upon reaching this temperature, 25 grams of hot acetic. anhydride, followed by 0.25 gram of concentrated sulfuric acid solution are added. The reaction requires 2 minutes. The product has a relative viscosity of 1.149. In a similar batch where only 0.1 gram of sulfuric acid is added, the reaction is complete 1n 9 minutes. This product has a relative viscosity of 1.136.

1 Example III Five (5) grams of cotton liners are added to 100 grams of dimethylacetamide. agitated and heated to anhydride are then added. gram of concentrated sulfuric plete in 3 minutes. product is 1.279.

A similar batch in which the sulfuric acid is reduced to 0.1 gram produces a product with a relative viscosity of 1.241 in a reaction period of 10 minutes.

The products of each of readily. Each is thereafter sub ected to conventlonal The resulting slurry is C. 25 grams of hot acetic This is followed by 0.25 acid. The reaction is com- The relative viscosity of the final to 20 minutes before adding the catalyst. Naturally, this period and will be dependent upon the type of cellulose, the particular amide, the temperature employed, and the like.

After the slurry has been brought up to temperature, the esterifying agent, e. g., acetic or other acid anhydride is stirred into will vary considerably procedure.

Although the reaction occurs at a high temperature and with extreme rapidity, it has been found to yield cellulose esters of excellent quality, characterized by uniformity, high molecular Weight with no evidence of substantial undesired side reactions.

The N,N'dialkylamides preferred as reaction media are the short chain N,N-dialkyl substituted amides of the lower fatty acids. Particularly effective among these are the short chain N,N-dialkyl substituted derivatives of formamide and acetamide. Among such. compounds may be mentioned N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and the like.

Any cellulose suitable fined cotton linters, high cose rayon and the like,

it may be activated for esterification, such as realpha-cellulose wood pulp, vismay be employed. If desired, known procedures.

present to afford a readily agitated slurry. In general, there should be about twenty times by weight more liquid than cellulose.

While the order of addition of the catalyst and the esterifying agent to the slurry of cellulose in amide is not critical, it has been found advantageous to add all of the esterifying agent prior to addition of the acid catalyst. Any of the usual esterifying agents such as the lower fatty acids or their anhydrides are suitable as are mixtures thereof. Among such acids and anbe mentioned those of acetic, propionic, and butyric. While the optimum ratio of esterifying agent to cellulose ,will depend on many factors, it has been found convenient to employ from four to ten times as much esterifying agent, i. e., acid or acid anhydride, by weight of cellulose.

Any conventional organic or inorganic acid esterification catalyst may be used. The mineral acids are most generally employed. Sulfuric acid is preferred due to its rapid action, low cost and ease of handling. As little as 0.1% by weight of sulfuric acid based on the total reactants has been found effective. Larger amounts, 5%, may sometimes be found desirhydrides may up to as much as able.

Many other modifications within the inventive concept, without a departure therefrom, will be apparent to those skilled in the art.

What is claimed is:

1. A process for the esterification of cellulose comprising the steps of commingling cellulose with a short chain N,N-dialkyl substituted amide of a lower fatty acid, heating and then adding lower fatty acid esterifying agent and a strong inorganic acid catalyst.

2. The process as defined in claim lower fatty acid is a member of the class consisting of formic and acetic.

3. The process as defined in claim 2 wherein the N,N-dialkylamide is N,N-dialkylformamide.

4. The process as defined in claim 3 wherein the N,N-dialkylformamide is N,N-dimethylformamide.

5. The process as defined in claim 3 wherein the N,N-dialkylformamide, is N,N-diethylformamide.

6. The process as defined in claim 2 wherein the N,N-dialkylamide is N,N-dialkylacetamide.

7. The process as defined in claim 6 wherein the N,N-dialkylacetamide is N,N-dimethylacetamide.

8. The process as defined in claim 6 wherein the N,N-dialkylacetamide is N,N-diethylacetamide.

9. The process as defined in claim 2 wherein the catalyst is sulfuric acid.

1 wherein the 10. A process for the esterification of cellulose comprising the steps of commingling unactivated cellulose with a short chain N,N-dialkyl substituted amide of a lower fatty acid, heating and then adding acetylating agent and a strong inorganic acid catalyst.

11. A process as defined in claim 10 wherein the lower fatty acid is a member of the class consisting of formic and acetic and the alkyl substituent is a methyl group.

12. The process as defined in claim 10 wherein the N,N-dialkylamide is N,N-dimethylformamide.

13. The process as defined in claim 10 wherein the N,N-dialkylamide is N,N-dimethylacetamide.

14. A process as defined in claim 10 wherein the lower fatty acid is a member of the class consisting of formic and acetic and the alkyl substituent is an ethyl group.

15. The process as defined in claim 10 wherein the N,N-dialkylamide is N,N-diethylformamide.

16. The process as defined in claim 10 wherein the N,N-dialkylamide is N,N-diethylacetamide.

17. A process for the acetylation of cellulose comprising the steps of commingling unactivated cellulose with a short chain N,N-dialkyl substituted amide of a lower fatty acid, heating and then adding acetic anhydride and a strong inorganic acid catalyst.

18. The process as defined in claim 17 wherein the cellulose and the amide are heated to at least about 100 C. before addition of acetic anhydride and acid catalyst.

19. The process as defined in claim 18 wherein the cellulose and amide are heated at the elevated temperature for from about ten to about twenty minutes before the addition of the acetic anhydride and the catalyst.

20. The process as defined in claim 19 wherein the acid catalyst is sulfuric acid.

References Cited in the file of this patent UNITED STATES PATENTS 40 2,536,634 Fraizy Jan. 2, 1951 2,631,144 Hiller Mar. 10, 1953 2,632,007 Blume et al. Mar. 17, 1953 OTHER REFERENCES Heuser: The Chemistry of Cellulose, John Wiley &

Sons, Inc., September 1947, pages 228 and 256. 

1. A PROCESS FOR THE ESTERIFICATION OF CELLULOSE COMPRISING THE STEPS OF COMMINGLING CELLULOSE WITH A SHORT CHAIN N,N-DIALKYL SUBSTITUTED AMIDE OF A LOWER FATTY ACID, HEATING AND THEN ADDING LOWER FATTY ACID ESTERIFYING AGENT AND A STRONG INORGANIC ACID CATALYST. 